Fuel-injector nozzles for supplying atomised droplets of liquid fuel to a combustion chamber in a gas-turbine engine are already known. One example is described in European patent application EP 1139021, which was published on 4 Oct. 2001 and involves the same inventor as the present application. FIGS. 1-3 of EP 1139021 are reproduced here as FIGS. 1-3 of this present application.
FIG. 1 shows a combustor for a gas-turbine engine, comprising a burner 10, a swirler 12, a pre-chamber 14 and a main combustion chamber 16. The swirler 12 includes a number of vanes 18 (see also FIG. 2) defining intervening passages 20, which are fed with compressed air from a manifold 22. The combustor may run off liquid fuel, in which case liquid fuel is introduced through nozzles 24 at the burner face 26. The nozzles 24 can operate in two different modes depending on the load condition. At high load the feed pressure, and hence the flow through the nozzle, is high enough to achieve good atomization of the fuel without the nozzle being electrically charged. However, at low load the flow is reduced and therefore the atomization is impaired. Hence, as the load is decreased, the voltage applied in the nozzle is increased, giving rise to enhanced atomization.
FIG. 2 is a plan view of the swirler 12 and burner 10 and showing the injection nozzles 24 arranged circumferentially around the burner, while FIG. 3 shows an injection nozzle 24 in greater detail. The nozzle 24 comprises a nozzle body 26 having a circular-section spin chamber 28. Liquid fuel is fed into the spin chamber 28 through an array of slots 30 and is thrown out through a throat 32 and passage 34, which is frustoconical in shape, in direction A to an outlet orifice 36. Due to the strong swirling movement of the fuel in the spin chamber, the fuel tends to keep to the inside surface 38 of the passage 34 and is atomised to faun small droplets as it expands out of the passage 34 into the air stream present in the swirler passages 20.
A tubular, electrically conductive electrode 40 is provided near the outlet end of the nozzle 24. The electrode 40 has a sharp edge 42, which extends in the direction of travel of the fuel through the nozzle. Insulating layers 44, 46 are provided on respective sides of the electrode 40.
The fuel is subjected to an electrostatic charge at the point where the fuel stream, which keeps to the inside wall 38, starts to break up into droplets as it exits the outlet 36. A charge supply and control unit 48 (see FIG. 1) feeds the electrode 40 with a voltage via an annular conductor 50.
Electrostatic charging of the fuel is beneficial mainly when the engine is running at low loads, i.e. when less fuel is being delivered to the nozzles 24. Such charging then helps to control the atomisation and vaporisation of the fuel, the fuel placement and combustion intensity. By contrast, it may not be necessary to employ electrostatic charging when the engine is running at full load.
The fuel-injection nozzle disclosed in EP 1139021 has the drawback that it is complex and thereby costly to manufacture. In addition the volume occupied by the nozzle is quite large, especially in the axial direction.